The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Referring now to FIG. 1, a functional block diagram is shown of a plasma processing system 10. Plasma processing system 10 includes RF generator 12 that provides RF power for a plasma chamber 14. A matching network 16 communicates the RF power to plasma chamber 14. Matching network 16 includes a variable capacitance module 26 that determines a tuning range and resolution of impedances for matching network 16.
Referring briefly to FIG. 2, a schematic diagram is shown of a portion of variable capacitance module 26. Variable capacitance module 26 includes a first adjustable capacitor 18-1 and a second adjustable capacitor 18-2, collectively referred to as capacitors 18. Capacitors 18 are adjusted by respective stepper motors 20-1 and 20-2 such that an output impedance of matching network 16 matches an input impedance of plasma chamber 14.
Returning to FIG. 1, matching network 16 includes a phase and magnitude detection module 22. Phase and magnitude detection module 22 generates signals based on respective ones of the phase and magnitude of the RF power from RF generator 12. Phase and magnitude detection module 22 communicates the signals to a control module 24 and communicates the RF power to variable capacitance module 26. Variable capacitance module 26 communicates the RF power to fixed inductance and capacitance (LC) module 28. Fixed LC module 28 cooperates with variable capacitance module 26 to vary the impedance of matching network 16. Fixed LC module 28 also communicates the RF power to an output sensing module 30. Output sensing module 30 generates signals based on the respective magnitude and/or phase of the RF power that is communicated to plasma chamber 14. The signals are communicated to a performance monitoring module 32 that performs diagnostic monitoring functions.
Control module 24 also generates stepper motor control signals that are communicated to respective ones of motors 20. The stepper motor control signals are based on the signals from phase and magnitude detection module 22, performance monitoring module 32, and/or user input settings.
Referring now to FIG. 3A, a graph 40 shows a relationship between a user input setting for capacitor 18-1 and an associated number of steps or position for motor 20-1. The user input setting for 100% capacitance is shown at 42. The user input setting for 0% capacitance is shown at 44. A vertical axis 46 indicates the number of steps for motor 20-1. A horizontal axis 48 indicates the number of steps for motor 20-2. Graph 40 shows that the user input settings (e.g. 42 and 44) for capacitor 18-1 are associated with respective numbers of steps for motor 20-1 independent of the position of motor 20-2 (and hence, the capacitance of capacitor 18-2).
Referring now to FIG. 3B, a graph 50 shows a relationship between a user input setting for capacitor 18-2 and the associated number of steps or position of motor 20-2. The user input setting for 100% capacitance is shown at 52. The user input setting for 0% capacitance is shown at 54. A vertical axis 56 indicates the number of steps for motor 20-2. A horizontal axis 58 indicates the number of steps for motor 20-1. Graph 50 shows that the user input settings (e.g. 52 and 54) for capacitor 18-2 are associated with respective numbers of steps for motor 20-2 independent of the position of motor 20-1 (and hence, the capacitance of capacitor 18-1).
Referring now to FIG. 4, a Smith chart 60 illustrates an effect of the motor position and capacitance relationships that are shown in FIGS. 3A and 3B. Generally the minimum and maximum capacitances of capacitors 18 are chosen such that matching network 16 has enough range to allow tuning to several impedances on the Smith chart 60. An example tuning range is shown at 62. The range 62 may be much larger than what is needed to tune to a single impedance 64 during operation. Since range 62 may be larger than what is needed the adjustment resolutions of capacitors 18 may also be more coarse than necessary.